1. Field of the Invention
The invention relates to a roller apparatus for soil compaction in accordance with the preamble of patent claim 1.
2. Description of the Related Art
For the compaction of soils, road surfaces or the like, compaction rollers are known which compact the ground as they travel over it by means of the load of one or more cylindrical xe2x80x9croller tiresxe2x80x9d and in some cases also by means of additional vibration. Depending on the type and design of the compaction roller, the individual roller tires can each be embodied as a non-driven, freely rolling towed roller tire or as a driven roller tire contributing to the propulsion of the compaction roller.
In addition to the type and composition of the ground to be compacted and the operational state of the compaction roller, the slip of the roller tires, in particular, has a pronounced influence on the degree of compaction and the quality of the compacted surface. The term xe2x80x9cslipxe2x80x9d is borrowed from automotive engineering and corresponds to a difference in speed between a shell or rolling surface of the roller tire and the soil.
Insufficient, generally negative slip therefore means that the peripheral speed of the roller tire is lower than the horizontal speed at which the roller tire moves over the soil. It arises especially in the case of non-driven, towed roller tires, as these, because of their inertia and rolling resistance, rotate more slowly than would be necessary for rolling on top of the soil. As a consequence of negative slip, accumulations of material may be formed in front of the roller (xe2x80x9cbulldozing effectxe2x80x9d) and, depending on the operating conditions, may be rolled over at irregular intervals, which results in an uneven, undulating surface. On the other hand, with negative slip, transverse cracks may be formed in the surface behind the roller tire as a result of tractive stresses in the soil, these also being known as xe2x80x9croller cracksxe2x80x9d; although they can be closed at the surface by subsequent rolling, they can hardly ever be eliminated.
An excessive, usually positive slip, such as frequently occurs with driven roller tires, can in some cases result in scuffing or gouging behind the roller tire. On the other hand, excessive slip may also, depending on the composition of the ground, give rise to the risk of reloosening of the compacted soil behind the roller tire.
The optimum slip for soil compaction depends both on the operating state of the compaction roller and on the type and composition of the ground. In practice, it is impossible to predetermine a clear, constant value for optimum slip under different operating conditions on different soils.
Further problems are caused by slip behavior in the case of roller apparatuses having a plurality of driven roller tires, as in such cases it must always be expected that at least one of the tires will have excessive or inadequate slip.
It is an object of the invention to provide a roller apparatus for soil compaction in which, irrespective of the operating state of the apparatus or of the state of the soil, optimum slip is always set automatically.
The solution to this problem is as defined in claim 1. Advantageous further developments of the invention will be found in the dependent claims.
The roller apparatus according to the invention comprises a determining device, by means of which it is possible to determine a vertical distance between a surface of the compacted soil lying behind the first roller tire, in other words a surface that has just been rolled, and a lowest point of the first roller tire, in other words the lower apex of the cylindrical roller tire. A speed of rotation adjustment device is able to set, as a function of the distance, the speed of rotation of the roller tire to be adjusted.
With the proviso that the distance is defined as positive when the surface of the compacted soil lies at a higher vertical level than the lowest point of the roller tire, in other words that the roller tire is producing a build-up of soil behind it, which corresponds to positive slip, the speed of rotation adjustment device reduces the speed of rotation when the distance is above a predetermined upper limiting value. Correspondingly, when the distance is negative, in other words the surface of the compacted soil lies at a lower vertical level than the lowest point of the roller tire, which corresponds to negative slip, the speed of rotation adjustment device can increase the speed of rotation when the distance is below a predetermined lower limiting value.
In a particularly advantageous embodiment of the invention, the upper and lower limiting values are identical and correspond to a slightly positive value which is just in excess of zero. This makes it possible to take account of the fact that the compacted soil, because of its elasticity, springs back after being rolled over by the roller tire, so that even when no slip takes place the distance must take on anxe2x80x94albeit lowxe2x80x94positive value, as the sprung-back surface of the compacted soil lies at a higher vertical level than the lower apex of the roller tire.
In a further advantageous embodiment of the invention, a distance measurement device is provided whereby the length of a vertical distance between the surface of the soil and a reference point on the roller apparatus can be measured. The determining device is then able to calculate the vertical distance as the difference between a lengthwise value, predetermined by the mechanical structure of the roller apparatus, and already stored in the determining device, for a vertical distance between the reference point and the lowest point, in other words the lower apex, of the roller tire and the vertical distance measured by the distance measurement device.
The slip control system according to the invention can be used particularly advantageously with a roller apparatus in which, apart from the controlled roller tire, at least one further roller tire driven in rotation is present. The additional roller tire then serves, inter alia, to support the force or torque for the first, controlled roller tire.
Advantageously, the controlled roller tire, viewed in the direction of travel of the roller apparatus, is the rearmost of all the driven roller tires.